Build a small piano with Arduino, eight buttons, and a buzzer, with the ability to record a played tune and replay it automatically with the same timing.
Wire a real NEO-6M GPS module to Arduino to extract coordinates and calculate the distance to a defined point.
Store temperature and humidity sensor readings in a text file on an SD card connected to NodeMCU for later review.
Build an electronic door lock system that verifies a passcode via keypad and drives a servo motor to lock and unlock.